Formation of boride barrier layers using chemisorption techniques

ABSTRACT

In one embodiment, a method for depositing a boride-containing barrier layer on a substrate is provided which includes exposing the substrate sequentially to a boron-containing compound and a tungsten precursor to form a first boride-containing layer during a first sequential chemisorption process, and exposing the substrate to the boron-containing compound, the tungsten precursor, and ammonia to form a second boride-containing layer over the first boride-containing layer during a second sequential chemisorption process. In one example, the tungsten precursor contains tungsten hexafluoride and the boron-containing compound contains diborane. In another embodiment, a contact layer is deposited over the second boride-containing layer. The contact layer may contain tungsten and be deposited by a chemical vapor deposition process. Alternatively, the contact layer may contain copper and be deposited by a physical vapor deposition process. In other examples, boride-containing layers may be formed at a temperature of less than about 500° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 10/993,925, filedNov. 19, 2004, and issued as U.S. Pat. No. 7,208,413, which is acontinuation of U.S. Ser. No. 10/387,990, filed Mar. 13, 2003, issued asU.S. Pat. No. 6,831,004, which is a continuation of U.S. Ser. No.09/604,943, filed Jun. 27, 2000, issued as U.S. Pat. No. 6,620,723,which are all herein incorporated in their entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the formation of boride barrier layersand, more particularly to boride barrier layers formed usingchemisorption techniques.

2. Description of the Related Art

In the manufacture of integrated circuits, barrier layers are often usedto inhibit the diffusion of metals and other impurities into regionsunderlying such barrier layers. These underlying regions may includetransistor gates, capacitor dielectric, semiconductor substrates, metallines, as well as many other structures that appear in integratedcircuits.

For the current sub-micron (0.5 μm) generation of semiconductor devices,any microscopic reaction at an interface between interconnection layerscan cause degradation of the resulting integrated circuits (e.g.,increase the resistivity of the interconnection layers). Consequently,barrier layers have become a critical component for improving thereliability of interconnect metallization schemes.

Compounds of refractory metals such as, for example, nitrides, borides,and carbides have been suggested as diffusion barriers because of theirchemical inertness and low resistivity (e.g., resistivity typically lessthan about 200 μΩ-cm). In particular, borides such as, for example,titanium diboride (TiB₂) have been suggested for use as a barriermaterial since layers formed thereof generally have low resistivity(e.g., resistivity less than about 150 μΩ-cm).

Boride barrier layers are typically formed using chemical vapordeposition (CVD) techniques. For example, titanium tetrachloride (TiCl₄)may be reacted with diborane (B₂H₆) to form titanium diboride using CVD.However, when Cl-based chemistries are used to form boride barrierlayers, reliability problems can occur. In particular, boride layersformed using CVD chlorine-based chemistries typically have a highchlorine content (e.g., chlorine content greater than about 3%). A highchlorine content is undesirable because the chlorine may migrate fromthe boride barrier layer into adjacent interconnection layers, which canincrease the contact resistance of such interconnection layers andpotentially change the characteristics of integrated circuits madetherefrom.

Therefore, a need exists in the art for reliable boride barrier layersfor integrated circuit fabrication. Particularly desirable would bereliable boride barrier layers useful for interconnect structures.

SUMMARY OF THE INVENTION

Boride barrier layers for integrated circuit fabrication are provided.In one embodiment, the boride barrier layer comprises one refractorymetal. The boride barrier layer may be formed by sequentiallychemisorbing alternating monolayers of a boron compound and a refractorymetal compound onto a substrate.

In an alternate embodiment, a composite boride barrier layer is formed.The composite boride barrier layer comprises two or more refractorymetals. The composite boride barrier layer may be formed by sequentiallychemisorbing monolayers of a boron compound and two or more refractorymetal compounds onto a substrate.

The boride barrier layer is compatible with integrated circuitfabrication processes. In one integrated circuit fabrication process,the boride barrier layer comprises one refractory metal. The boridebarrier layer is formed by sequentially chemisorbing alternatingmonolayers of a boron compound and one refractory metal compound on asubstrate. Thereafter, one or more metal layers are deposited on theboride barrier layer to form an interconnect structure.

In another integrated circuit fabrication process, the boride barrierlayer has a composite structure. The composite boride barrier layercomprises two or more refractory metals. The composite boride barrierlayer is formed by sequentially chemisorbing monolayers of a boroncompound and two or more refractory metal compounds on a substrate.Thereafter, one or more metal layers are deposited on the compositeboride barrier layer to form an interconnect structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 depicts a schematic illustration of an apparatus that can be usedfor the practice of embodiments described herein;

FIGS. 2A-2C depict cross-sectional views of a substrate structure atdifferent stages of integrated circuit fabrication incorporating aboride barrier layer;

FIGS. 3A-3C depict cross-sectional views of a substrate undergoing afirst sequential chemisorption process of a boron compound and onerefractory metal compound to form a boride barrier layer;

FIGS. 4A-4D depict cross-sectional views of a substrate undergoing asecond sequential chemisorption process of a boron compound and tworefractory metal compounds to form a composite boride barrier layer;

FIGS. 5A-5D depict cross-sectional views of a substrate undergoing athird sequential chemisorption of a boron compound and two refractorymetal compounds to form a composite boride barrier layer; and

FIGS. 6A-6C depict cross-sectional views of a substrate structure atdifferent stages of integrated circuit fabrication incorporating morethan one boride barrier layer.

DETAILED DESCRIPTION

FIG. 1 depicts a schematic illustration of a wafer processing system 10that can be used to form boride barrier layers in accordance withembodiments described herein. The system 10 comprises a process chamber100, a gas panel 130, a control unit 110, along with other hardwarecomponents such as power supplies 106 and vacuum pumps 102. The salientfeatures of process chamber 100 are briefly described below.

Chamber 100

The process chamber 100 generally houses a support pedestal 150, whichis used to support a substrate such as a semiconductor wafer 190 withinthe process chamber 100. Depending on the specific process, thesemiconductor wafer 190 can be heated to some desired temperature priorto layer formation.

In chamber 100, the wafer support pedestal 150 is heated by an embeddedheater 170. For example, the pedestal 150 may be resistively heated byapplying an electric current from an AC power supply 106 to the heaterelement 170. The wafer 190 is, in turn, heated by the pedestal 150, andcan be maintained within a desired process temperature range of, forexample, about 20° C. to about 500° C.

A temperature sensor 172, such as a thermocouple, is also embedded inthe wafer support pedestal 150 to monitor the temperature of thepedestal 150 in a conventional manner. For example, the measuredtemperature may be used in a feedback loop to control the electriccurrent applied to the heater element 170 by the power supply 106, suchthat the wafer temperature can be maintained or controlled at a desiredtemperature that is suitable for the particular process application. Thepedestal 150 is optionally heated using radiant heat (not shown).

A vacuum pump 102 is used to evacuate process gases from the processchamber 100 and to help maintain the desired pressure inside the chamber100. An orifice 120 is used to introduce process gases into the processchamber 100. The dimensions of the orifice 120 are variable andtypically depend on the size of the process chamber 100.

The orifice 120 is coupled to a gas panel 130 via a valve 125. The gaspanel 130 provides process gases from two or more gas sources 135, 136to the process chamber 100 through orifice 120 and valve 125. The gaspanel 130 also provides a purge gas from a purge gas source 138 to theprocess chamber 100 through orifice 120 and valve 125.

A control unit 110, such as a computer, controls the flow of variousprocess gases through the gas panel 130 as well as valve 125 during thedifferent steps of a wafer process sequence. Illustratively, the controlunit 110 comprises a central processing unit (CPU) 112, supportcircuitry 114, and memories containing associated control software 116.In addition to the control of process gases through the gas panel 130,the control unit 110 is also responsible for automated control of thenumerous steps required for wafer processing—such as wafer transport,temperature control, chamber evacuation, among other steps.

The control unit 110 may be one of any form of general purpose computerprocessor that can be used in an industrial setting for controllingvarious chambers and sub-processors. The computer processor may use anysuitable memory, such as random access memory, read only memory, floppydisk drive, hard disk, or any other form of digital storage, local orremote. Various support circuits may be coupled to the computerprocessor for supporting the processor in a conventional manner.Software routines as required may be stored in the memory or executed bya second processor that is remotely located. Bi-directionalcommunications between the control unit 110 and the various componentsof the wafer processing system 10 are handled through numerous signalcables collectively referred to as signal buses 118, some of which areillustrated in FIG. 1.

Boride Barrier Layer Formation

FIGS. 2A-2C illustrate one preferred embodiment of boride layerformation for integrated circuit fabrication of an interconnectstructure. In general, the substrate 200 refers to any workpiece uponwhich film processing is performed, and a substrate structure 250 isused to generally denote the substrate 200 as well as other materiallayers formed on the substrate 200. Depending on the specific stage ofprocessing, the substrate 200 may be a silicon semiconductor wafer, orother material layer, which has been formed on the wafer. FIG. 2A, forexample, shows a cross-sectional view of a substrate structure 250,having a material layer 202 thereon. In this particular illustration,the material layer 202 may be an oxide (e.g., silicon dioxide). Thematerial layer 202 has been conventionally formed and patterned toprovide a contact hole 202H extending to the top surface 200T of thesubstrate 200.

FIG. 2B shows a boride layer 204 conformably formed on the substratestructure 250. The boride layer 204 is formed by chemisorbing monolayersof a boron-containing compound and a refractory metal compound on thesubstrate structure 250.

The monolayers are chemisorbed by sequentially providing aboron-containing compound and one or more refractory metal compounds toa process chamber. In a first sequential chemisorption process, themonolayers of the boron-containing compound and one refractory metalcompound are alternately chemisorbed on a substrate 300 as shown inFIGS. 3A-3C.

FIG. 3A depicts a cross-sectional view of a substrate 300, which may bein a stage of integrated circuit fabrication. A monolayer of aboron-containing compound 305 is chemisorbed on the substrate 300 byintroducing a pulse of a boron-containing gas into a process chambersimilar to that shown in FIG. 1. The boron-containing compound typicallycombines boron atoms 310 with one or more reactive species b 315. Duringboride layer formation, the reactive species b 315 form byproducts thatare transported from the surface of substrate 300 by the vacuum system.

The chemisorbed monolayer of the boron-containing compound 305 isself-limiting in that only one monolayer may be chemisorbed onto thesurface of substrate 300 during a given pulse. Only one monolayer of theboron-containing compound is chemisorbed on the substrate because thesubstrate has a limited surface area. This limited surface area providesa finite number of sites for chemisorbing the boron-containing compound.Once the finite number of sites is occupied by the boron-containingcompound, further chemisorption of the boron-containing compound will beblocked.

The boron-containing compound may be for example a borane compoundhaving the general formula B_(x)H_(y), where x has a range between 1 and10, and y has a range between 3 and 30. For example, borane (BH₃),diborane (B₂H₆), triborane, tetraborane, pentaborane, hexaborane,heptaborane, octaborane, nonaborane, and decaborane, may be used as theboron-containing compound.

After the monolayer of the boron compound is chemisorbed onto thesubstrate 300, excess boron-containing compound is removed from theprocess chamber by introducing a pulse of a purge gas thereto. Purgegases such as, for example, helium, argon, nitrogen (N₂), ammonia (NH₃),and hydrogen (H₂), among others may be used.

After the process chamber has been purged, a pulse of one refractorymetal compound is introduced into the process chamber. Referring to FIG.3B, a layer of the refractory metal compound 307 is chemisorbed on theboron monolayer 305. The refractory metal compound typically combinesrefractory metal atoms 320 with one or more reactive species a 325.

The chemisorbed monolayer of the refractory metal compound 307 reactswith the boron-containing monolayer 305 to form a boride layer 309. Thereactive species a 325 and b 315 form byproducts ab 330 that aretransported from the substrate 300 surface by the vacuum system. Thereaction of the refractory metal compound 307 with the boron monolayer305 is self-limited, since only one monolayer of the boron compound waschemisorbed onto the substrate 300 surface.

The refractory metal compound may include refractory metals such as forexample titanium, tungsten, tantalum, zirconium, hafnium, molybdenum,niobium, vanadium, and chromium, among others combined with reactivespecies such as, for example chlorine and fluorine. For example,titanium tetrachloride (TiCl₄), tungsten hexafluoride (WF₆), tantalumpentachloride (TaCl₅), zirconium tetrachloride (ZrCl₄), hafniumtetrachloride (HfCl₄), molybdenum pentachloride (MoCl₅), niobiumpentachloride (NbCl₅), vanadium pentachloride (VCl₅), chromiumtetrachloride (CrCl₄) may be used as the refractory metal compound.

After the monolayer of the refractory metal compound is chemisorbed ontothe substrate 300, any excess refractory metal compound is removed fromthe process chamber by introducing another pulse of the purge gastherein. Thereafter, as shown in FIG. 3C, the boride layer depositionsequence of alternating monolayers of the boron-containing compound andthe refractory metal compound are repeated until a desired boride layerthickness is achieved. The boride layer may, for example, have athickness in a range of about 200 Å to about 5,000 Å, and morepreferably, about 2,500 Å.

In FIGS. 3A-3C, boride layer formation is depicted as starting with thechemisorption of a boron-containing monolayer on the substrate followedby a monolayer of a refractory metal compound. Alternatively, the boridelayer formation may start with the chemisorption of a monolayer of arefractory metal compound on the substrate followed by a monolayer ofthe boron-containing compound.

The pulse time for each pulse of the boron-containing compound, the oneor more refractory metal compounds, and the purge gas is variable anddepends on the volume capacity of the deposition chamber as well as thevacuum system coupled thereto. Similarly, the time between each pulse isalso variable and depends on the volume capacity of the process chamberas well as the vacuum system coupled thereto.

In general, the alternating monolayers may be chemisorbed at a substratetemperature less than about 500° C., and a chamber pressure less thanabout 100 Torr. A pulse time of less than about 1 second for theboron-containing compound, and a pulse time of less than about 1 secondfor the refractory metal compounds are typically sufficient to chemisorbthe alternating monolayers that comprise the boride layer on thesubstrate. A pulse time of less than about 1 second for the purge gas istypically sufficient to remove the reaction byproducts as well as anyresidual materials remaining in the process chamber.

In a second chemisorption process, the boron-containing monolayers andtwo or more refractory metal compounds are alternately chemisorbed onthe substrate to form a composite boride layer. FIG. 4A depicts across-sectional view of a substrate 400, which may be in a stage ofintegrated circuit fabrication. A self-limiting monolayer of aboron-containing compound 405 is chemisorbed on the substrate 400 byintroducing a pulse of a boron-containing compound into a processchamber similar to that shown in FIG. 1 according to the processconditions described above with reference to FIGS. 2A-2C. Theboron-containing compound combines boron atoms 410 with one or morereactive species b 415.

After the monolayer of the boron compound 405 is chemisorbed onto thesubstrate 400, excess boron-containing compound is removed from theprocess chamber by introducing a pulse of a purge gas thereto.

Referring to FIG. 4B, after the process chamber has been purged, a pulseof a first refractory metal compound M₁a₁ is introduced into the processchamber. A layer of the first refractory metal compound 407 ischemisorbed on the boron monolayer 405. The first refractory metalcompound typically combines first refractory metal atoms M₁ 420 with oneor more reactive species a₁ 425.

The chemisorbed monolayer of the first refractory metal compound 407reacts with the boron-containing monolayer 405 to form a boridemonolayer 409. The reactive species a₁ 425 and b 415 form byproducts a₁b430 that are transported from the substrate 400 surface by the vacuumsystem.

After the monolayer of the first refractory metal compound 407 ischemisorbed onto the substrate 400, the excess first refractory metalcompound M₁a₁ is removed from the process chamber by introducing anotherpulse of the purge gas therein.

Another pulse of the boron-containing compound is than introduced intothe process chamber. A monolayer of the boron-containing compound 405 ischemisorbed on the first refractory metal monolayer 407, as shown inFIG. 4C. The chemisorbed monolayer of the boron-containing compound 405reacts with the first refractory metal monolayer 407 to form a boridelayer 409. The reactive species a₁ 425 and b 415 form byproducts a₁b 430that are transported from the substrate 400 surface by the vacuumsystem.

After the monolayer of the boron compound 405 is chemisorbed onto thefirst refractive metal monolayer 407, excess boron-containing compoundis removed from the process chamber by introducing a pulse of a purgegas thereto.

Referring to FIG. 4D, after the process chamber has been purged, a pulseof a second refractory metal compound M₂a₁ is introduced into theprocess chamber. A layer of the second refractory metal compound ischemisorbed on the boron monolayer 405. The second refractory metalcompound typically combines second refractory metal atoms M₂ 440 withone or more reactive species a₁ 425.

The chemisorbed monolayer of the second refractory metal compound reactswith the boron-containing monolayer 405 to form the composite boridelayer 409. The reactive species a₁ 425 and b 415 form byproducts a₁b 430that are transported from the substrate 400 surface by the vacuumsystem.

After the monolayer of the second refractory metal compound ischemisorbed onto the substrate 400, the excess second refractory metalcompound M₂a₁ is removed from the process chamber by introducing anotherpulse of the purge gas therein.

Thereafter, the boride layer deposition sequence of alternatingmonolayers of the boron-containing compound and the two refractory metalcompounds M₁a₁ and M₂a₁ are repeated until a desired boride layerthickness is achieved.

In FIGS. 4A-4D, boride layer formation is depicted as starting with thechemisorption of the boron-containing monolayer on the substratefollowed by monolayers of the two refractory metal compounds.Alternatively, the boride layer formation may start with thechemisorption of monolayers of either of the two refractory metalcompounds on the substrate followed by monolayers of theboron-containing compound. Optionally, monolayers of more than tworefractory metal compounds may be chemisorbed on the substrate 400.

In a third chemisorption process, the boron-containing monolayers andtwo or more refractory metal compounds are alternately chemisorbed onthe substrate to form a composite boride layer, as illustrated in FIGS.5A-5D.

FIG. 5A depicts a cross-sectional view of a substrate 500, which may bein a stage of integrated circuit fabrication. A self-limiting monolayerof a first refractory metal compound 507 is chemisorbed on the substrate500 by introducing a pulse of a first refractory metal compound M₁a₁into a process chamber similar to that shown in FIG. 1 according to theprocess conditions described above with reference to FIGS. 2A-2C.

After the monolayer of the first refractory metal compound 507 ischemisorbed onto the substrate 500, excess first refractory metalcompound is removed from the process chamber by introducing a pulse of apurge gas thereto.

Referring to FIG. 5B, after the process chamber has been purged, a pulseof a second refractory metal compound M₂a₁ is introduced into theprocess chamber. A layer of the second refractory metal compound 511 ischemisorbed on the first refractory metal monolayer 507.

After the monolayer of the second refractory metal compound 511 ischemisorbed onto the substrate 500, the excess second refractory metalcompound M₂a₁ is removed from the process chamber by introducing anotherpulse of the purge gas therein.

A pulse of a boron-containing compound 510 is than introduced into theprocess chamber. A monolayer of the boron-containing compound 505 ischemisorbed on the second refractory metal monolayer 511, as shown inFIG. 5C. The chemisorbed monolayer of the boron-containing compound 505reacts with the second refractory metal monolayer 511 to form acomposite boride layer 509. The reactive species a₁ 525 and b 515 formbyproducts a₁b 530 that are transported from the substrate 500 surfaceby the vacuum system.

After the monolayer of the boron compound 505 is chemisorbed onto thesecond refractory metal monolayer 511, excess boron-containing compoundis removed from the process chamber by introducing a pulse of a purgegas thereto.

Referring to FIG. 5D, after the process chamber has been purged, a pulseof the first refractory metal compound 520 M₁a₁ is introduced into theprocess chamber. A monolayer of the first refractory metal compound 507is chemisorbed on the boron monolayer 505.

The chemisorbed monolayer of the first refractory metal compound 507reacts with the boron-containing monolayer 505 to form the boridemonolayer 509. The reactive species a₁ 525 and b 515 form byproducts a₁b530 that are transported from the substrate 500 surface by the vacuumsystem.

After the monolayer of the first refractory metal compound 507 ischemisorbed onto the substrate 500, the excess first refractory metalcompound M₁a₁ is removed from the process chamber by introducing anotherpulse of the purge gas therein.

Thereafter, the boride layer deposition sequence of alternatingmonolayers of the boron-containing compound and the two refractory metalcompounds M₁a₁ (520) and M₂a₁ (540) are repeated until a desired boridelayer thickness is achieved.

In FIGS. 5A-5D, boride layer formation is depicted as starting with thechemisorption of the first refractory metal monolayer on the substratefollowed by monolayers of the second refractory metal compound and theboron-containing compound. Alternatively, the boride layer formation maystart with the chemisorption of the monolayer of the boron-containingcompound on the substrate followed by the monolayers of the tworefractory metal compounds. Optionally, monolayers of more than tworefractory metal compounds may be chemisorbed on the substrate 500.

The sequential deposition processes described above advantageouslyprovide good step coverage for the boride layer, due to the monolayerchemisorption mechanism used for forming the boride layer. Inparticular, boride layer formation using the monolayer chemisorptionmechanism is believed to contribute to a near perfect step coverage overcomplex substrate topographies.

Furthermore, in chemisorption processes, since only one monolayer may beabsorbed on the topographic surface, the size of the deposition area islargely independent of the amount of precursor gas remaining in thereaction chamber once a monolayer has been formed.

Referring to FIG. 2C, after the formation of the boride layer 204, acontact layer 206 may be formed thereon to complete the interconnectstructure. The contact layer 206 is preferably selected from the groupof aluminum, copper, tungsten, and combinations thereof.

The contact layer 206 may be formed, for example, using chemical vapordeposition (CVD), physical vapor deposition (PVD), or a combination ofboth CVD and PVD. For example, an aluminum layer may be deposited from areaction of a gas mixture containing dimethyl aluminum hydride (DMAH)and hydrogen (H₂) or argon or other DMAH containing compounds, a CVDcopper layer may be deposited from a gas mixture containing Cu⁺²(hfac)₂(copper hexafluoro acetylacetonate), Cu⁺²(fod)₂ (copper heptafluorodimethyl octanediene), Cu⁺¹(hfac)TMVS (copper hexafluoro acetylacetonatetrimethylvinylsilane), or combinations thereof, and a CVD tungsten layermay be deposited from a gas mixture containing tungsten hexafluoride. APVD layer is deposited from a copper target, an aluminum target, or atungsten target.

FIGS. 6A-6C illustrate an alternate embodiment of boride layer formationfor integrated circuit fabrication of the interconnect structure. Ingeneral, the substrate 600 refers to any workpiece upon which filmprocessing is performed, and a substrate structure 650 is used togenerally denote the substrate 600 as well as other material layersformed on the substrate 600. Depending on the specific stage ofprocessing, the substrate 600 may be a silicon semiconductor wafer, orother material layer, which has been formed on the wafer. FIG. 6A, forexample, shows a cross-sectional view of a substrate structure 650,having a material layer 602 thereon. In this particular illustration,the material layer 602 may be an oxide (e.g., silicon dioxide). Thematerial layer 602 has been conventionally formed and patterned toprovide a contact hole 602H extending to the top surface 600T of thesubstrate 600.

FIG. 6B shows two boride layers 604, 606 conformably formed on thesubstrate structure 650. The boride layers 604, 606 are formed bychemisorbing monolayers of a boron-containing compound and one or morerefractory metal compounds on the substrate structure 650 as describedabove with reference to FIGS. 3 a-5 d. The two boride layers 604, 606may each comprise one or more refractory metals. The thicknesses of thetwo or more boride layers 604, 606 may be variable depending on thespecific stage of processing. Each boride layer 604, 606 may, forexample, have a thickness in a range of about 200 Å to about 5,000 Å.

Referring to FIG. 6C, after the formation of the boride layers 604, 606,a contact layer 608 may be formed thereon to complete the interconnectstructure. The contact layer 608 is preferably selected from the groupof aluminum, copper, tungsten, and combinations thereof.

The specific process conditions disclosed in the above discussion aremeant for illustrative purposes only. Other combinations of processparameters such as precursor and inert gases, flow ranges, pressure andtemperature may also be used in forming the boride layer of the presentinvention.

Although several preferred embodiments, which incorporate the teachingsof the present invention, have been shown and described in detail, thoseskilled in the art can readily devise many other varied embodiments thatstill incorporate these teachings.

1. A method for depositing a boride-containing barrier layer on asubstrate, comprising: exposing a substrate sequentially and cyclicallyto a boron-containing compound, a purge gas, and a tungsten precursor toform a first boride-containing layer comprising tungsten and boronduring a first sequential chemisorption process; and exposing thesubstrate sequentially and cyclically to the boron-containing compound,an ammonia purge gas, and the tungsten precursor to form a secondboride-containing layer over the first boride-containing layer during asecond sequential chemisorption process.
 2. The method of claim 1,wherein the second sequential chemisorption process comprises: exposingthe substrate to the boron-containing compound; exposing the substrateto the ammonia purge gas; exposing the substrate to the tungstenprecursor; and exposing the substrate to the ammonia purge gas.
 3. Themethod of claim 1, wherein the second sequential chemisorption processcomprises: exposing the substrate to the boron-containing compound;exposing the substrate to the ammonia purge gas; and exposing thesubstrate to the tungsten precursor.
 4. The method of claim 1, whereinthe tungsten precursor comprises tungsten hexafluoride.
 5. The method ofclaim 4, wherein the boron-containing compound comprises diborane. 6.The method of claim 5, wherein a contact layer is deposited over thesecond boride-containing layer.
 7. The method of claim 6, wherein thecontact layer comprises tungsten and the contact layer is deposited by achemical vapor deposition process.
 8. The method of claim 6, wherein thecontact layer comprises copper and the contact layer is deposited by aphysical vapor deposition process.
 9. The method of claim 1, wherein thefirst boride-containing layer or the second boride-containing layer isformed at a temperature of less than about 500° C.
 10. The method ofclaim 9, wherein the temperature is about 400° C. or less.
 11. A methodfor depositing a boride-containing barrier layer on a substrate,comprising: exposing a substrate sequentially and cyclically to aboron-containing compound, an ammonia purge gas, and a tungstenprecursor to form a first boride-containing layer during a firstsequential chemisorption process; and exposing the substratesequentially and cyclically to the boron-containing compound, a purgegas, and the tungsten precursor to form a second boride-containing layerover the first boride-containing layer during a second sequentialchemisorption process.
 12. The method of claim 11, wherein the firstsequential chemisorption process comprises: exposing the substrate tothe boron-containing compound; exposing the substrate to the ammoniapurge gas; exposing the substrate to the tungsten precursor; andexposing the substrate to the ammonia purge gas.
 13. The method of claim11, wherein the first sequential chemisorption process comprises:exposing the substrate to the boron-containing compound; exposing thesubstrate to the ammonia purge gas; and exposing the substrate to thetungsten precursor.
 14. The method of claim 11, wherein the tungstenprecursor comprises tungsten hexafluoride.
 15. The method of claim 14,wherein the boron-containing compound comprises diborane.
 16. The methodof claim 15, wherein a contact layer is deposited over the secondboride-containing layer.
 17. The method of claim 16, wherein the contactlayer comprises tungsten and the contact layer is deposited by achemical vapor deposition process.
 18. The method of claim 16, whereinthe contact layer comprises copper and the contact layer is deposited bya physical vapor deposition process.
 19. The method of claim 11, whereinthe first boride-containing layer or the second boride-containing layeris formed at a temperature of less than about 500° C.
 20. The method ofclaim 19, wherein the temperature is about 400° C. or less.
 21. A methodfor depositing a boride-containing barrier layer on a substrate,comprising: exposing a substrate sequentially to diborane, a purge gascomprising helium, argon, and hydrogen, and tungsten hexafluoride toform a first boride-containing layer comprising tungsten and boronduring a first sequential chemisorption process; and exposing thesubstrate to the diborane, ammonia purge gas, and the tungstenhexafluoride to form a second boride-containing layer over the firstboride-containing layer during a second sequential chemisorptionprocess.